title: Human periventricular grey somatosensory evoked potentials suggest rostrocaudally inverted somatotopy.
abstract: BACKGROUND
  Somatosensory homunculi have been demonstrated in primary somatosensory cortex and ventral posterior thalamus but not periaqueductal and periventricular grey matter (PAVG), a therapeutic target for deep brain stimulation (DBS) in chronic pain.
  
  
  OBJECTIVE
  The study is an investigation of somatotopic representation in PAVG and assessment for a somatosensory homunculus.
  
  
  METHODS
  Five human subjects were investigated using electrical somatosensory stimulation and deep brain macroelectrode recording. DBS were implanted in the contralateral PAVG. Cutaneous arm, leg and face regions were stimulated while event-related potentials were recorded from deep brain electrodes. Electrode contact positions were mapped using MRI and brain atlas information.
  
  
  RESULTS
  Monopolar P1 somatosensory evoked potential amplitudes were highest and onset latencies shortest in contralateral caudal PAVG with facial stimulation and rostral with leg stimulation, in agreement with reported subjective sensation during intra-operative electrode advancement.
  
  
  CONCLUSIONS
  A rostrocaudally inverted somatosensory homunculus exists in the human PAVG region. Objective human evidence of PAVG somatotopy increases understanding of a brainstem region important to pain and autonomic control that is a clinical target for both pharmacological and neurosurgical therapies. Such knowledge may assist DBS target localisation for neuropathic pain syndromes related to particular body regions like brachial plexopathies, anaesthesia dolorosa and phantom limb pain.
authors.affiliation: Oxford Functional Neurosurgery and Experimental Neurology Group, Nuffield Department of Surgical Sciences, University of Oxford, Oxford, UK.
authors.forename: Erlick A C
authors.initials: EA
authors.lastname: Pereira
authors.forename: Shouyan
authors.initials: S
authors.lastname: Wang
authors.forename: Sarah L F
authors.initials: SL
authors.lastname: Owen
authors.forename: Tipu Z
authors.initials: TZ
authors.lastname: Aziz
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Green
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods*; D046690:Deep Brain Stimulation; D004567:Electrodes, Implanted; D005073:Evoked Potentials, Somatosensory; D005145:Face; D005260:Female; D006801:Humans; D007866:Leg; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009437:Neuralgia / Q000503:physiopathology / Q000628:therapy*; D010487:Periaqueductal Gray / Q000503:physiopathology; D012677:Sensation / Q000502:physiology; D013238:Stereotaxic Techniques; D013681:Tegmentum Mesencephali / Q000503:physiopathology*